drm/pagemap_util: Add a utility to assign an owner to a set of interconnected gpus

The hmm_range_fault() and the migration helpers currently need a common
"owner" to identify pagemaps and clients with fast interconnect.
Add a drm_pagemap utility to setup such owners by registering
drm_pagemaps, in a registry, and for each new drm_pagemap,
query which existing drm_pagemaps have fast interconnects with the new
drm_pagemap.

The "owner" scheme is limited in that it is static at drm_pagemap creation.
Ideally one would want the owner to be adjusted at run-time, but that
requires changes to hmm. If the proposed scheme becomes too limited,
we need to revisit.

v2:
- Improve documentation of DRM_PAGEMAP_OWNER_LIST_DEFINE(). (Matt Brost)

Signed-off-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Reviewed-by: Matthew Brost <matthew.brost@intel.com>
Acked-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com> # For merging through drm-xe.
Link: https://patch.msgid.link/20251219113320.183860-11-thomas.hellstrom@linux.intel.com

1 files changed, 50 insertions, 0 deletions

diff --git a/include/drm/drm_pagemap_util.h b/include/drm/drm_pagemap_util.h
index 924244d5b899..19169b42b891 100644
--- a/include/drm/drm_pagemap_util.h
+++ b/include/drm/drm_pagemap_util.h
@@ -6,11 +6,55 @@
 #ifndef _DRM_PAGEMAP_UTIL_H_
 #define _DRM_PAGEMAP_UTIL_H_
 
+#include <linux/list.h>
+#include <linux/mutex.h>
+
 struct drm_device;
 struct drm_pagemap;
 struct drm_pagemap_cache;
+struct drm_pagemap_owner;
 struct drm_pagemap_shrinker;
 
+/**
+ * struct drm_pagemap_peer - Structure representing a fast interconnect peer
+ * @list: Pointer to a &struct drm_pagemap_owner_list used to keep track of peers
+ * @link: List link for @list's list of peers.
+ * @owner: Pointer to a &struct drm_pagemap_owner, common for a set of peers having
+ * fast interconnects.
+ * @private: Pointer private to the struct embedding this struct.
+ */
+struct drm_pagemap_peer {
+	struct drm_pagemap_owner_list *list;
+	struct list_head link;
+	struct drm_pagemap_owner *owner;
+	void *private;
+};
+
+/**
+ * struct drm_pagemap_owner_list - Keeping track of peers and owners
+ * @peer: List of peers.
+ *
+ * The owner list defines the scope where we identify peers having fast interconnects
+ * and a common owner. Typically a driver has a single global owner list to
+ * keep track of common owners for the driver's pagemaps.
+ */
+struct drm_pagemap_owner_list {
+	/** @lock: Mutex protecting the @peers list. */
+	struct mutex lock;
+	/** @peers: List of peers. */
+	struct list_head peers;
+};
+
+/*
+ * Convenience macro to define an owner list.
+ * Typically the owner list statically declared
+ * driver-wide.
+ */
+#define DRM_PAGEMAP_OWNER_LIST_DEFINE(_name)	\
+	struct drm_pagemap_owner_list _name = {	\
+	  .lock = __MUTEX_INITIALIZER((_name).lock),	\
+	  .peers = LIST_HEAD_INIT((_name).peers) }
+
 void drm_pagemap_shrinker_add(struct drm_pagemap *dpagemap);
 
 int drm_pagemap_cache_lock_lookup(struct drm_pagemap_cache *cache);
@@ -39,4 +83,10 @@ static inline void drm_pagemap_shrinker_might_lock(struct drm_pagemap *dpagemap)
 
 #endif /* CONFIG_PROVE_LOCKING */
 
+void drm_pagemap_release_owner(struct drm_pagemap_peer *peer);
+
+int drm_pagemap_acquire_owner(struct drm_pagemap_peer *peer,
+			      struct drm_pagemap_owner_list *owner_list,
+			      bool (*has_interconnect)(struct drm_pagemap_peer *peer1,
+						       struct drm_pagemap_peer *peer2));
 #endif